The present invention relates to intravascular stent implants for maintaining vascular patency in humans and animals. More particularly, the present invention provides a radially-expandable stent and a delivery system for delivering a radially-expandable stent within a body lumen.
Percutaneous transluminal coronary angioplasty (PTCA) is used to increase the lumen diameter of a coronary artery partially or totally obstructed by a build-up of cholesterol fats or atherosclerotic plaque. Typically a first guidewire of about 0.038 inches in diameter is steered through the vascular system to the site of therapy. A guiding catheter, for example, can then be advanced over the first guidewire to a point just proximal of the stenosis. The first guidewire is then removed. A balloon catheter on a smaller 0.014 inch diameter second guidewire is advanced within the guiding catheter to a point just proximal of the stenosis. The second guidewire is advanced into the stenosis, followed by the balloon on the distal end of the catheter. The balloon is inflated causing the site of the stenosis to widen.
The dilatation of the occlusion, however, can form flaps, fissures and dissections which threaten reclosure of the dilated vessel or even perforations in the vessel wall. Implantation of a stent can provide support for such flaps and dissections and thereby prevent reclosure of the vessel or provide a patch repair for a perforated vessel wall until corrective surgery can be performed. It has also been shown that the use of intravascular stents can measurably decrease the incidence of restenosis after angioplasty thereby reducing the likelihood that a secondary angioplasty procedure or a surgical bypass operation will be necessary.
An implanted prosthesis such as a stent can preclude additional procedures and maintain vascular patency by mechanically supporting dilated vessels to prevent vessel reclosure. Stents can also be used to repair aneurysms, to support artificial vessels as liners of vessels or to repair dissections. Stents are suited to the treatment of any body lumen, including the vas deferens, ducts of the gallbladder, prostate gland, trachea, bronchus and liver. The body lumens range in diameter from small coronary vessels of 3 mm or less to 28 mm in the aortic vessel. The invention applies to acute and chronic closure or reclosure of body lumens.
A typical stent is a cylindrically shaped wire formed device intended to act as a permanent prosthesis. A typical stent ranges from 5 mm to 50 mm in length. A stent is deployed in a body lumen from a radially compressed configuration into a radially expanded configuration which allows it to contact and support a body lumen. The stent can be made to be radially self-expanding or expandable by the use of an expansion device. The self expanding stent is made from a resilient springy material while the device expandable stent is made from a material which is plastically deformable. A plastically deformable stent can be implanted during a single angioplasty procedure by using a balloon catheter bearing a stent which has been crimped onto the balloon. The stent expands radially as the balloon is inflated, forcing the stent into contact with the interior of the body lumen thereby forming a supporting relationship with the vessel walls.
Conventional angioplasty balloons fall into high, medium and low pressure ranges. Low pressure balloons are those which fall into rated burst pressures below 6 atmospheres. Medium pressure balloons are those which fall into rated burst pressures between 6 and 12 atmospheres. High pressure balloons are those which fall into rated burst pressures above 12 atmospheres. Burst pressure is determined by material selection, wall thickness and tensile strength.
The biocompatible metal stent props open blocked coronary arteries, keeping them from reclosing after balloon angioplasty. A balloon of appropriate size and pressure is first used to open the lesion. The process is repeated with a stent crimped on a second balloon. The second balloon may be a high pressure type of balloon, e.g., more than 12 atmospheres, to insure that the stent is fully deployed upon inflation. The stent is deployed when the balloon is inflated. The stent remains as a permanent scaffold after the balloon is withdrawn. A high pressure balloon is preferable for stent deployment because the stent must be forced against the artery""s interior wall so that it will fully expand thereby precluding the ends of the stent from hanging down into the channel encouraging the formation of thrombus.
Various shapes of stents are known in the art. U.S. Pat. No. 4,649,922 (Wiktor) discloses a linearly expandable spring-like stent. U.S. Pat. No. 4,886,062 (Wiktor) discloses a two-dimensional zigzag form, typically a sinusoidal form. U.S. Pat. No. 4,969,458 (Wiktor) discloses a stent wire coiled into a limited number of turns wound in one direction, then reversed and wound in the opposite direction with the same number of turns, then reversed again and so on until a desired length is obtained.
Stents have limited ability to provide effective patching of perforated vessels due to the spacing between metal elements. U.S. Pat. No. 4,878,906 (Lindeman et al.) describes an endoprosthesis made of a thin wall molded plastic sleeve intended to be collapsed radially and delivered to a damaged area of a vessel where it is expanded to provide a sealed interface to the vessel on its outer peripheral ends. The endoprosthesis therefore provides a patch which prevents leakage of blood from a vessel wall. The endoprosthesis disclosed employs various molded-in ribs, struts and the like to adapt the device for particular applications and to provide the desired degree of stiffness to form the sealed interface with the vessel wall. Such a stiff prosthesis, however, could not be expected to have the longitudinal flexibility needed to adapt to curved vessels.
One problem with self-expanding stents is that the stents must be compressed into a small diameter for delivery to the site or portion of the body lumen at which support is desired. It is preferable that the stents be compressed into as small of a diameter as possible (typically referred to as xe2x80x9cprofilexe2x80x9d) to assist in delivering the stent to the desired site. That compression can, in some cases cause localized areas of high bending stress/strain within the stent.
As a result of the high bending stresses/strain, the minimum profile for the self-expanding stents can be limited to prevent non-recoverable strain levels in the stent and, therefore, ensure full radial expansion of the stent when released from the delivery system. The larger profile can limit the delivery and use of the stent to larger diameter lumens.
Alternatively, if a small delivery profile is desired, then the stent may be designed to achieve that profile which can often result in a larger window area and a reduction in the outward forces generated by the stent after expansion within the lumen. The larger window area and, therefore, inferior body lumen scaffolding reduces the effectiveness against recurring restenosis. The reduced outward forces may be problematic if the stent does not firmly engage the wall of the lumen.
One attempt at addressing the high bending stresses/strains in a self-expanding stent is described in U.S. Pat. No. 4,830,003 (Wolff et al.) in which the stent is made of a series of generally straight wire segments welded together at their ends to form a zigzag shaped stent when expanded. By using generally straight wires, the bending stresses/strains associated with bends in an integral wire-formed stent body can be avoided. Disadvantages associated with this approach include, however, the cost of manufacturing the stents by welding. The welds also lower the allowable stress levels in the stent, thereby limiting its fatigue life and compression for delivery. Another disadvantage is that the length of the stent can change significantly from the compressed state to the expanded state, thereby making accurate placement of the stent at the desired location within a body lumen more difficult.
Another attempt at addressing the high bending stresses/strains includes manufacturing self-expanding stents from materials other than metals as described in, e.g., U.S. Pat. No. 5,356,423 (Tihon et al.). The stents disclosed therein are formed of thermoplastic materials and can be molded or otherwise formed into a fenestrated pattern similar to those produced by braided wire stents. By shaping the openings as depicted in FIG. 5 of the patent, the stress concentration at the bending points can be reduced. Disadvantages of this approach include, however, degradation associated with implanted plastic materials, including changes in the elasticity of the plastics which can result in a reduction in the radially outward forces generated by the stent.
It is an object of the invention to provide a self-expanding stent for implantation within a body lumen that provides for reductions in the bending stresses/strains associated with compression of the stent for delivery to the desired location within a body lumen.
It is another object of the present invention to provide a self-expanding stent in which the longitudinal length of the stent remains unchanged from the compressed state to the expanded state.
It is a further object of the invention to provide a stent with improved longitudinal flexibility to allow for threading through tortuous lumens and lesions, as well as to permit implantation in highly curved lumens.
It is an object of some delivery systems according to the present invention to provide a delivery system in which the position of the stent can be fixed relative to a guide catheter.
It is another object of some delivery systems according to the present invention to provide a balloon integral with the stent delivery device to allow for post-deployment dilatation of the stent without removing the stent delivery catheter.
It is another object of some delivery systems of the present invention to provide for simplified threading of a guidewire through a distal portion of a rapid-exchange delivery system.
In one aspect, the present invention provides radially expandable stent for implantation within a body lumen including an elongated generally tubular body defining a passageway having a longitudinal axis; the body including a plurality of circumferential support sections arranged successively along the longitudinal axis, each of the support sections having a length along the longitudinal axis; each of the circumferential support sections including a plurality of primary bends interconnected by struts, the primary bends being located on alternating ends of the support section around the circumference of the body, each of the struts connecting successive primary bends on opposite ends of the support section and having a midpoint generally located therebetween; and at least one longitudinal member connecting adjacent support sections in the body, the longitudinal member having a first end attached proximate the midpoint of one of the struts and a second end attached proximate the midpoint of one of the struts in the adjacent support section; wherein the stent is radially compressible into a compressed state in which the struts are generally aligned with the longitudinal axis and radially expandable into an expanded state in which the struts and the primary bends in each of the support sections are arranged in a zigzag pattern, and further wherein the longitudinal length of the stent in the compressed state is substantially the same as the longitudinal length of the stent in the expanded state.
In another aspect the present invention provides a self-expanding radially expandable stent for implantation within a body lumen including an elongated generally tubular body defining a passageway having a longitudinal axis, the body including at least one circumferential support section having a length along the longitudinal axis; each of the circumferential support sections including a plurality of primary bends interconnected by struts, the primary bends being located on alternating ends of the support section around the circumference of the body, each of the struts connecting successive primary bends on opposite ends of the support section and having a midpoint generally located therebetween; wherein the stent is radially compressible into a compressed state and radially expandable into an expanded state in which the struts and primary bends in each of the support sections are arranged in a zigzag pattern, and further wherein each pair of adjacent struts associated with each of the primary bends abut at a point between the primary bend and the midpoint of each strut in the pair of adjacent struts when the stent is in the compressed state, whereby the bending stress is reduced at each primary bend of the plurality of primary bends.
In another aspect, the present invention provides a self-expanding radially expandable stent for implantation within a body lumen including an elongated generally tubular body defining a passageway having a longitudinal axis, the body including at least one circumferential support section having a length along the longitudinal axis; each of the circumferential support sections including a substantially continuous element including a plurality of primary bends interconnected by struts, the primary bends being located on alternating ends of the support section around the circumference of the body, each of the struts connecting successive primary bends on opposite ends of the support section and having a midpoint generally located therebetween, wherein the stent is radially compressible into a compressed state and radially expandable into an expanded state in which the struts and primary bends in each of the support sections are arranged in a zigzag pattern; and means for reducing bending stress at the primary bends when the stent is in the compressed state.
In another aspect, the present invention provides a delivery system for implantation of a radially-expandable stent within a body lumen including an inner tube having a proximal end and a distal end, the inner tube having an inner tube lumen formed therein, the inner tube lumen having an opening at the distal end of the inner tube; a cover sheath having a proximal end and a distal end, the cover sheath comprising a wall defining a cover sheath lumen, the inner tube located within the cover sheath lumen; a stent positioned about the inner tube at the distal end of the cover sheath; a first guidewire opening in the inner tube lumen, the first guidewire opening spaced from the distal end of the inner tube; a second guidewire opening in the wall of the cover sheath, the second guidewire opening located proximate the first guidewire opening; and a guide element having a distal end located within the inner tube lumen, the guide element extending between the first and second guidewire openings.
In another aspect, the present invention provides a method of deploying a stent within a body lumen by providing a radially expandable stent on a delivery system including an inner tube having a proximal end and a distal end, the inner tube having an inner tube lumen formed therein, the inner tube lumen having an opening at the distal end of the inner tube and a first guidewire opening in the inner tube lumen, the first guidewire opening spaced from the distal end of the inner tube; a stent positioned on the exterior surface of the inner tube at the distal end of the inner tube; a cover sheath having a proximal end and a distal end, the cover sheath comprising a wall defining a cover sheath lumen, the inner tube and stent located within the cover sheath lumen, the cover sheath further including a second guidewire opening in the wall of the cover sheath, the second guidewire opening located proximate the first guidewire opening in the inner tube; and a guide element having a distal end located within the inner tube lumen, the guide element extending between the first and second guidewire openings, wherein the guide element comprises a guide lumen formed in the distal end of the guide element; positioning a guidewire within a body lumen, wherein a proximal end of the guidewire extends out of the body lumen; inserting the proximal end of the guidewire into the inner tube lumen at the distal end of the inner tube; advancing the proximal end of the guidewire through the inner tube lumen towards the first guidewire opening and the distal end of the guide element, wherein at least a portion of the proximal end of the guidewire is advanced into the guide lumen in the distal end of the guide element; advancing the proximal end of the guidewire through the first and second guidewire openings; advancing the distal end of the inner tube and the stent over the guidewire towards the distal end of the guidewire, wherein the stent is positioned at a desired location within the body lumen; and deploying the stent at the desired location within the body lumen.
In another aspect, the present invention provides a method of deploying a stent within a body lumen by providing a radially expandable stent on a delivery system including an inner tube having a proximal end and a distal end, the inner tube having an inner tube lumen formed therein; a stent positioned on the exterior surface of the inner tube at the distal end of the inner tube; an expandable balloon located on the inner tube; an inflation lumen in fluid communication with the balloon, the inflation lumen extending from the proximal end of the delivery system to the balloon; and a cover sheath having a proximal end and a distal end, the cover sheath comprising a wall defining a cover sheath lumen, the inner tube, stent, and balloon located within the cover sheath lumen; positioning the inner tube, stent, balloon and cover sheath within a body lumen; moving the cover sheath proximally relative to the distal end of the inner tube to deploy the stent with the body lumen; and inflating the balloon within the stent.
In another aspect, the present invention provides a method of deploying a stent within a body lumen by providing a radially expandable stent on a delivery system including an inner tube having a proximal end and a distal end; a stent positioned on the exterior surface of the inner tube at the distal end of the inner tube; a cover sheath having a proximal end and a distal end, the cover sheath including a cover sheath lumen, the inner tube and stent located within the cover sheath lumen; and a support tube having a proximal end and a distal end, the support tube including a support tube lumen containing at least a portion of the proximal end of the cover sheath, the cover sheath being movable in the proximal and distal directions within the support tube lumen and the position of the inner tube being fixed relative to the position of the support tube; positioning a guide catheter within a body lumen; advancing the distal ends of the inner tube and the cover sheath through the guide catheter; fixing the position of the support tube relative to the guide catheter, wherein the positions of the distal end of the inner tube and the stent within the body lumen are also fixed relative to the guide catheter; and moving the cover sheath proximally to release the stent on the distal end of the inner tube, thereby deploying the stent within the body lumen.
These and other features and advantages of the present invention are described below in connection the description of the preferred embodiments.